Range scanners as for example laser scanners may be used to generate a digital representation of a surface of an object. Typically, range scanners generate an output indicative of 3D coordinates of each of a plurality of points. The result of scanning an object is therefore a collection of points, also called a point cloud.
An interesting application of such a method and apparatus includes the generation of a data mapping of the internal surface of the ear and ear canal, so that 3-dimensional data or a digital model of the internal surface of the ear and ear canal can be obtained. Such a 3-dimensional model can be used to produce a shell, which has the exact shape of the canal and the shell may form the basis for an In-The-Ear (ITE) or Completely-In-The-Canal (CIC) hearing aid. Also ear moulds or shells for other purposes such as a hearing protection or for headsets may be produced from the data model. The shell can be produced on the basis of the data model in different ways, such as by recent developed rapid prototyping methods or by well known machining, e.g. in a Computer Numerically Controlled (CNC) machining centre.
The advantage of having a data model of the ear canal, e.g. compared to traditional manufacturing processes based on ear impressions taken by introducing a semi-fluent, curable material into the ear canal, is that the production of the shell can take place at any location. This in turn allows a centralisation of the shell production at a central production facility, thereby facilitating the maintenance of a uniform quality. Further so the data model may be transmitted either as it is obtained or right thereafter for evaluation at a production facility. Thereby a data model of the hearing aid may be generated, which may be realized based on the dimensions and shape of the canal. The data model of the hearing aid can be transmitted back to the end user for visual evaluation.
International patent application WO 02/091920 discloses a method and apparatus for obtaining geometrical data relating to the internal surface of the ear and ear canal of the human body in order to be able to generate a model of the internal surface of the ear and ear canal. To this end this prior art document discloses a probe having a longitudinal axis, where light is emitted from a mirror at the tip of the probe in a right angle away from the longitudinal axis of the probe and towards the surrounding canal wall. The apparatus comprises a detector for detecting reflected light from the canal wall, and analysing means for determining the distance from the probe to the internal surface of the canal at points of the circumference.
The point cloud data resulting from the scanning process of a surface of an object may be further processed on a data processing system so as to generate another digital representation of the surface, such as a triangulated surface. This process is called surface reconstruction.
Hence, once the entire surface of an object has been scanned by means of a scanner, a surface reconstruction process may be performed on a computer allowing a reconstructed surface to be displayed and saved. However, in certain circumstances the scanner is operated by a user during the scanning, e.g. when using a hand-held scanner that is constructed as a combined ranger scanner and 3D position system, or a scanner with a handheld probe, In such situations, it is desirable that the user operating the scanner receives some kind of feedback during scanning so as to allow the user to determine whether sufficient data has been obtained and/or whether all parts of the surface have been sufficiently covered by the scanning process. In particular, it would generally be desirable for the user to be able to see a 3D model of the surface already scanned. Unfortunately, due to the massive amount of computation required for surface reconstruction, it is very difficult to generate surface reconstructions during scanning, i.e. in real-time or near real-time.